State Machine

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A simple, yet powerful state machine framework for Dart supporting Flutter and web apps.

This library is open source, stable and well tested. Development happens on GitHub. Feel free to report issues or create a pull-request there. General questions are best asked on StackOverflow.

The package is hosted on dart packages. Up-to-date class documentation is created with every release.

Tutorial

Installation

Follow the installation instructions on dart packages.

Import the package into your Dart code using:

import 'package:statemachine/statemachine.dart';

Creating a machine

To create a new state machine instantiate Machine:

var machine = Machine<String>();

The type of the state machine is used to uniquely identify states of the machine. In this simple example we use a String; but typically you would define an enum, a Symbol, or an arbitrary other identifying object.

Defining states

To create states call Machine.newState and store them in variables. The first state created it the start state of the machine. Each state needs an identifying key of the declared type, in this case we use simple strings that help debugging:

var startState = machine.newState('start');
var activeState = machine.newState('active');

It is possible to explicitly create start and stop states of the machine using Machine.newStartState and Machine.newStopState.

Callbacks on states

States support callbacks whenever a state is entered or left.

activeState.onEntry(() => print('activated'));
activeState.onExit(() => print('deactivate'));

Starting and stopping a machine

To start a state machine and set its state to its starting state call Machine.start:

machine.start();

Similarly, you can stop a machine by calling Machine.stop.

Transitioning between states

There are various ways in which your machine can switch states.

Manually triggered transition

From anywhere within your code you can enter a specific state by calling State.enter.

activeState.enter();

Depending on context, it might be easier to set the current state using the accessor on the state machine itself:

machine.current = activeState;

Alternatively, you can also use the identifying object to set the active state:

machine.current = 'active';

Event triggered transition

You can define transitions between states that are triggered by events of any kind using State.onStream. The example below registers for click events when the inactive state is entered. In case of a click event the callback is executed, and the state machine transitions into the active state:

startState.onStream(element.onClick, (value) => activeState.enter());

Future completion transition

Also, transitions can be triggered by the completion of a future using State.onFuture. Since futures cannot be suspended or cancelled, the future continues to run even if the owning state is deactivated. Should the state be activated, and the future value is already present, then the value is immediately supplied into the callback. Further activations have no effect.

startState.onFuture(computation, (value) => activeState.enter());

Time based transition

Also, you can automatically trigger callbacks after a timeout using State.onTimeout. The following snippet calls the callback 1 second after the active state is entered and falls back to the inactive state:

activeState.onTimeout(Duration({seconds: 1}), () => startState.enter());

Callbacks often contain code to check for additional constraints and update other objects or UI element before entering a different state. See the tooltip example directory for a more complete illustration of the functionality provided by this library.

Nested machines

Machines can be nested. Simply add another machine that gets started when the state is entered, and stopped when the state is left.

activeState.addNested(anotherMachine);

Misc

Resources

License

The MIT License, see LICENSE.

Libraries

statemachine
Generic state machine framework.